Carbon nanotube is a substance in which a graphene sheet made of carbon forms a monolayer- or multilayer-coaxial tube, and is a material that has ultrafine diameter, lightweight, high mechanical strength, high flexibility, high current density, high thermal conductivity, and high electric conductivity. By spinning such carbon nanotube into a thread, it is expected that a fibrous material with unprecedented properties can be obtained.
Such carbon nanotube spinning methods can be divided roughly into a gas phase method and a liquid phase method. A gas phase method is a method in which a spinning process directly follows the carbon nanotube synthesis process, thereby performing the synthesis and spinning of carbon nanotube simultaneously. On the other hand, the liquid phase method is a method in which a pre-synthesized carbon nanotube powder is dissolved in a liquid, and the dispersed carbon nanotube is spun to form a thread-like fibrous carbon nanotube. Thus, it is a method wherein synthesis and spinning are performed in separate processes.
As the gas phase method, for example, a method in which a catalyst for carbon nanotube synthesis and hydrocarbon that serves as a raw material for carbon nanotube are provided to a cylindrical reactor along with a carrier gas, thereby allowing carbon nanotube to grow, which is then spun onto a spindle in a non-reactive area of the reactor to obtain a carbon nanotube fiber, is disclosed (see Patent Document 1).
Further, as the liquid phase method, a method in which a carbon nanotube dispersion of low viscosity, wherein carbon nanotube is uniformly dispersed, is discharged into a viscous dispersion containing poly vinyl alcohol (PVA) etc. with a steady flow, to obtain a composite fiber of carbon nanotube and PVA, is disclosed (see Patent Document 2).
Furthermore, as another liquid phase method, a method in which a carbon nanotube dispersion of low viscosity, wherein carbon nanotube is uniformly dispersed, is discharged into a dispersion of strong acid or strong alkali (with pH 3 or less or pH 11 or more), to obtain a nanofiber, is disclosed (see Patent Document 3).